“Invisible: Covert Operations and Classified Landscapes,” a new book by the artist Trevor Paglen, is an album of the visual side of these secret worlds. Paglen’s “Limit Photography” series offers glimpses of classified military installations, most of them in southwestern states, some of them thousands of square miles in size. Their uses range from combat training to the testing of “unacknowledged weapons.” To photograph facilities deep in these restricted regions, Paglen used high-powered binoculars and astrophotography lenses, sometimes positioning himself on mountaintops. In another series, “The Other Night Sky,” Paglen photographed classified spacecraft in Earth orbit, borrowing tracking techniques from a global network of amateur astronomers who have catalogued the nearly two hundred such objects currently in space.

The photographs in both series are somewhat abstract, sometimes blurry, giving them a haunted, ephemeral feel. “At extreme distances, there is essentially no such thing as depth of field,” Paglen notes. “No matter how ambiguous or elusive the images in this book are, however, the underlying landscapes are quite real.” They also represent a great deal of money. “The blank spots on the map that Paglen describes have their corollary in the blank spots in the mind and in public dialogue,” Rebecca Solnit writes in her introduction. “We do not debate the development of new systems of killing, the militarization of space, or the cost of our military budget, and most of us know little or nothing about the programs in question.” The Post, WikiLeaks, and Paglen have filled in a few of those blank spots. The debate is up to us.